Magnetostriction is a property of ferromagnetic materials that causes them to change shape when subjected to a magnetic field. Magnetostrictive materials can convert magnetic energy into kinetic energy, or the reverse, and are used to build various actuators and sensors.
Magnetostrictive sensors have been developed for nondestructive materials testing that make use of magnetostrictive properties of the material under inspection. Magnetostrictive sensors designed for testing ferromagnetic materials can also be made to work for testing nonferromagnetic metals by attaching a ferromagnetic material to the material being tested at areas where the sensors are to be placed. This may be achieved, for example, by coating the surface of the material to be tested with a coat of ferromagnetic material or by bonding a ferromagnetic medium such as wire or ribbon to the surface of the material.
The combination of a magnetized magnetostrictive material and an excitation coil produces a magnetostrictive sensor (MsS) probe. For active non-destructive testing, elastic waves are launched and reflected echoes of the waves from defects such as corrosion or cracks are detected. A typical application of an MsS probe is for inspecting pipes and tubes, the primary structural members used in various industries to transport gaseous or liquid products. Various MsS probes have been designed to generate longitudinal waves in rods and cables, torsional waves in pipes, and shear horizontal waves in plates.